The present invention relates generally to surgical cutting instruments and, more particularly, to microsurgical cutting instruments and an improved cutting probe assembly therefor.
In microsurgery, particularly ophthalmic surgery, smooth cutting action of the vitreous tissue is highly desirable. Many types of surgical cutting instruments for aiding ophthalmic physicians have been proposed. In general, microsurgical instruments of this kind include a cutting probe assembly insertable into the patient. The cutting probe assembly can be inserted into the eye, through an incision in the cornea or sclera. Included in such a probe assembly are generally coaxially extending inner and outer cutting members. A port or opening extends radially through the outer cutting member adjacent a distal end thereof and through which tissue is aspirated for subsequent cutting and continued aspiration. Disposed for movement within the outer cutting member is the inner cutting member which cooperates with the former for effecting the cutting action.
It has been determined that when the motion of the inner cutting member is rotational relative to the outer cutting member, the vitreous and other tissue have an undesirable tendency of being pulled while being cut. Current practice prefers providing a reciprocating longitudinally moving inner cutting member that moves relative to a cutting port of the outer cutting member. This provides a cleaner chopping or guillotine type of action to the tissue drawn through the port. Many drive systems are available for reciprocating the inner cutting member, such as disclosed in U.S. Pat. Nos. 4,246,902 and 4,674,502. Many of the known microsurgical cutting instruments of the latter type have the inner and outer cutting members reciprocate along a common axis with sufficient radial clearance therebetween (e.g. a few thousandths of an inch) to effect the desired cutting or shearing action on the tissue. For successful cutting it, is important to have a predetermined cutting clearance between the reciprocating coaxial members. However, this is often difficult to achieve on a consistent basis. In U.S., Pat. No. 4,210,146 there is disclosed a surgical instrument having a bendable spring-type inner cutting blade which changes in shape as it reciprocates along a path and engages a tapered configuration of an inner wall of the outer member. Another known approach described generally in U.S. Pat. No. 4,696,298 is to flare the end of the inner cutting member into an elliptical shape so as to achieve a spring-tension in order to hold the cutting blade into conformity with the inner diameter of the outer member.
From the foregoing, it is clear that there is a continuing effort to improve the cutting efficiency of microsurgical cutting instruments by attempting to provide a constant and clean shearing cut in an inexpensive and reliable manner.